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https://hdl.handle.net/2142/22170
Description
Title
Liquid metal brushes for homopolar devices
Author(s)
Talmage, Gita
Issue Date
1989
Doctoral Committee Chair(s)
Walker, John S.
Department of Study
Engineering, Mechanical
Discipline
Engineering, Mechanical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
Design predictions for liquid metal current collectors require a thorough knowledge of liquid metal flows in a narrow gap between a fixed surface and a moving surface, with a strong applied magnetic field and with a free surface beyond each moving end of the gap. The radial and axial velocities in the secondary flow are reduced by a strong axial or radial magnetic field. For a sufficiently strong field, the azimuthal momentum transport by the secondary flow can be neglected. This assumption reduces the problem for a primary azimuthal velocity to a fully developed magnetohydrodynamic (MHD) duct flow problem with a moving wall and two free surfaces.
For laminar flows, we observed the interaction between the electromagnetic body forces and the viscous shear stresses due to the Couette flow for arbitrary Hartmann numbers. Under special conditions, distinct regions of flow emerge. Of particular interest are the high speed velocity jets that arise in the free shear layers. The physical insight that we developed by analyzing laminar flows carried over into turbulent flows.
A typical current collector device can have a Reynolds number, based on the rotor velocity and radial gap width, well within a turbulent flow regime. Now that a theory that models turbulence in the presence of a magnetic field exists we can study interaction between the MHD effects and the turbulence.
Our one- and two-dimensional MHD results indicate that turbulence in the presence of a magnetic field has a profound effect on both the velocity and electric potential distributions. However, for the parameter range currently of interest, an ordinary hydrodynamic model for turbulence is sufficient. We observed that the magnitude of the velocity is reduced and the profile flattened for fully turbulent flows as compared with laminar flows. In MHD flows, a reduction in the magnitude of the velocity is equivalent to a decrease in the electrical resistance. Therefore, as a consequence of the velocity decrease, the magnitude of the current density increases for a given voltage difference between the rotor and the stator.
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